Spring means



Nov. 29, 1966 YUKIHIRO TAKATSU 3,288,457

srnzme MEANS Filed Oct. 6, 1964 2 Sheets-Sheet 1 FIG. I

FIG

& 53 4s 53 INVENTOR.

United States Patent 3,288,457 SPRING MEANS Yukihiro Takatsu,Yokohama-shi, Japan, assignor to Nippon Halsujo Kabushiki Kaisha, NHKSpring Co., Ltd., Yokohama-shi, Japan Filed Oct. 6, 1964, Ser. No.401,817 4 Claims. (Cl. 267-48) This invention relates to an improvementin a spring means, and particularly to a spring means for heavy loadearring wheels of a vehicle such as the rear wheels of a truck.

In general, a progressive spring has such a load characteristic curve asis shown in the solid line in FIG. 12. In order to increase the springconstant in accordance with an increase in load and at the same time toequalize the force applied to a main spring with that applied to anauxiliary spring at the maximum load, such an auxiliary spring must haveleaves with an appreciably high rigidity. To this end, an appreciablythick filat steel leaf is required. However, practically speaking, thethickness of a fiat steel leaf is limited so that, in order to give theauxiliary spring the desired characteristic, more and more leaves arerequired to be laminated to give the necessary rigidity to the auxiliaryspring.

If the problem with respect to stress is satisfied, a small number ofthick flat spring leaves is more advantageous than a large number ofthin flat spring leaves. This fact will be illustrated by comparing onesheet of thick flat steel with two sheets of thin flat steel as follows:

If a spring constant required for an auxiliary spring is 2/01, aone-leafed spring is indicated by a sufiix 1, and a two-leafed spring isindicated by a suffix 2, the length L of the second leaf of thetwo-leafed spring is 0.6 of that of the first leaf so as to give auniform stress thereto, and these are equal,

kn=3EI /L (1) in case of the one-leafed spring, and

kn=3EI /(L O.568) (2) in case of the two-leafed spring. From (1) and (2)I =I /0.568 Hence b t /l2:(b t 3/12) (1/0.568)

Since b =b O.828=t2/t1 Now the weights will be compared with each otherby way of comparing volumes:

The volume of one-leafed spring V rbL and the volume of two-leafedspring Vg=lgbL+tb X =0.828t bL( 1 +0.6)

=1.325r bL From (4) and (5),

That is to say, in case of a one-leafed spring, it merely weighs about3/4 of that of a corresponding two-leafed spring. Thus it is to beunderstood that in view of the weight, it is more advantageous to adopta less number of thicker leaves than a more number of thinner leaves in3,288,457 Patented Nov. 29, 1956 "ice order to obtain a leaf springhaving a desired spring constant. However, practically speaking, becauseof limits set on the dimensions of flat steels for spring use, desirablythick flat steel is unavailable, so that it is rather usual to be forcedto design such a leaf spring by laminating more leaves one upon anotherthat is unduly heavy. Thus it has been unavoidable that the weight and,accordingly, the material cost and manufacturing expense areunreasonably high.

One object of this invention is to provide a spring means which is ableto overcome the drawbacks as referred to above.

Another object of this invention is to provide a spring means whichmakes more comfortable the driving of a truck or the like.

Still another object of this invention is to provide a spring meanswhich is more wear resistant so as to render a truck or the like onwhich it is used more durable.

Further another object of this invention is to provide a spring meanswhich does not creak.

Briefly stated in accordance with one aspect of this invention, there isprovided a spring means comprising a main spring and an auxiliaryspring. The main spring comprises a number of leaf springs laminated oneupon another in a well known manner. The auxiliary spring, so-calledhelper in the art, in accordance with the present invention comprises anumber of bar steel springs hereinafter described. The bar may be eithera round bar or a round bar having lateral vertical flat sides. The barsteel springs vertically have less curvature than the curvature of theleaf springs, are arranged longitudinally side by side at intervals, arefastened integrally with each other by uniting means at the proximity ofthe both longitudinal ends and at the center of the auxiliary spring,and are attached to the main spring in such a manner that the centers ofthe bar springs are contacted with the central bottom surface of thelowermost one of the leaf springs.

The invention will be better understood and other objects and additionaladvantages of the invention will become apparent upon perusal of thefollowing description taken in connection with the drawings in which:

FIG. 1 is a side elevational view of a spring embodying this invention;

FIG. 2 is a bottom view thereof;

FIG. 3 is a cross-sectional view, enlarged, taken along lines 3-3 ofFIG. 2;

FIG. 4 is an enlarged front elevational view thereof;

FIG. 5 is a perspective view of another embodiment of this invention;

FIG. 6 is a side elevational view thereof;

FIG. 7 is a bottom view thereof;

FIG. 8 is a cross-sectional view, enlarged, taken along lines 88 of FIG.7;

FIG. 9 is a graph of the load charactaeris-tics both of the springs ofthe invention and of certain prior art springs;

FIG. 10 is graph illustrating the relation of deflection to load;

FIG. 11 is a cross-sectional view of a round bar having lateral verticalfiat sides; and

FIG. 12 is a graph similar to FIG. 9 but showing another embodiment.

Referring more particular-to FIGS. 1 through 4, a main spring 21 isshown comprising a number of leaf springs 21a. An auxiliary spring, theso-called helper, comprises two round bar steel springs 23. The roundbar springs 23 vertically have less curvature than the curvature of theleaf springs 21a of the main spring 21. Both ends of the round bar steelspring 23 are tapered horizontally at the lower side 25 whereby theauxiliary spring is made more easily deflectable when it comes intocontact with the lowermost leaf spring 27 of the main spring 21. The tworound bar steel springs 23 are arranged longitudinally side by side witha space between. A center bolt 29 is provided extending through theleaves 21a of the main spring 21 and a channel adapting member 31engaged by a nut 29a on the bolt 29 which holds the two round bar steelsprings 23 in such a manner that the center of the latter are contactedwith the central bottom surface of the lowermost leaf spring 27. Thecenter bolt 29 is freely inserted through a collar 33 between thelowermost leaf spring 27 and the channel adapting member 31. It is to benoted that the collar 33 is slightlyshorter than the diameter of theround bar steel spring 23 so that the bar steel spring 23 contacts thelowermost leaf spring 27 directly and so that it can be inserted in thespace between the round bar steel springs 23. The ends of the round barsteel springs 23 are spaced from each other by means of spacers 35,respectively. By virture of the space 37 provided between the two roundbar steel springs 23, it is possible to keep the upper surfaces of theround bar steel springs 23 free from dust naturally and also to providethe space for the center bolt 29 and the collar 33. By virtue of thespacers 35, the longitudinal ends of the round bar steel springs 23 areheld and prevented from any individual motion.

The embodiment just set forth will be compared with the prior art. Inthe leaf springs in accordance with prior art, those which have only oneauxiliary spring are most advantageous in view of the weight advantageas set forth hereinbefore. Such a leaf spring will now be compared withthis embodiment just described.

If a spring constant required for the auxiliary springs is 21m and thesuflix for the flat steel is f, and for the round bar steel is r,

kn=3EI /L (6) in case of fiat steel as (1), and

kn=3E x 2I /L (7) in case of round bar steel. From (6) and (7) I ZIHence bt 12:2 x 1rd d 64 Hence bt =31rd /8 (8) If the weights arecompared with each other by comparing volumes:

Now in case d: 1.153t, from Equation 8,

bt :3/8 x 1r x (1.1530 bz =3/8 x 11' x 1.7551

Hence Meantime, in view of the dimension of the available flat steel,b/t 5. Therefore, the case d=1.153t cannot be, but necessarily dl.153t.' Therefore, V; V That is to say, the use of flat steel isnecessarily disadvantageous comparing with the use of round bar steel.

The above comparison has been made for the most advantageous case offiat steel or for such a case where only one flat steel auxiliary springis used. However, practically speaking, more than two flat steel springsare used so that the weight becomes more than 4/3. Therefore, comparingwith this embodiment, the value of d in flat steel becomes at least morethan 4/3 1.153 1.55. Thus it will be seen that this embodiment is faradvantageous.

Other than the above comparison from the point of view of weight, thereis a great advantage for round bar steel so that such a material havinga large value for I is available and desirable load characteristics maybe given to a progressive spring. In FIG. 9 the above comparison isillustrated. The dotted line in FIG. 12 represents a characteristicachieved by the embodiment. While the prior art springs have beenstrictly restricted in their load characteristics, such restrictions donot obtain with the springs in accordance with the present invention.

Further comparison will now be made referring to some dimensions for thepractical design of progressive springs as follows:

If the following conditions,

2L=900 mm. b= mm. 2P =1200 kg.

a load whereby the auxiliary spring first comes in contact with the mainspring 250 kg,

km.+h= 17 kg./mm. and

p =85 kg./mm.

are to be satisfied in a design, reference may be had to Table I.

TAB LE I Auxiliary Spring of Round Bar Auxiliary Spring of Flat SteelSteel is provided is provided Leaf N o.

T x b L W kg. t x b L W kg.

5 x 50 900 1. 75 5 x 50 900 1. 75 5 x 50 900 1. 75 5 x 50 900 1. 75 5 x50 860 1. 67 5 x 50 860 1.67 5 x 50 810 1. 57 5 x 50 810 1. 57 5 x 50760 1.47 5 x 50 760 1.47 5 x 50 710 1.38 5 x 50 710 1. 38 5 x 50 660 1.28 5 x 50 660 1. 28 5 x 50 610 1.18 5 x 50 610 1.18 Aux. Spring 20 x 2a560 2. 71 15.6 x 50 560 3. 03

From (8) and (9) V /V, =3/4 x d /z Therefore, if

d l l 5 3t, t r

The total weight becomes 14.76 kg. in case where round 5 bar steel isused for the auxiliary springs while the corresponding weight is 15.35kg. in case where fiat steel is used. In these cases, the springconstants kn=5.5 and kn+h= 17.1, and the load whereby the auxiliarysprings first come in contact with the main spring becomes 350 kg. andthe load whereby the auxiliary springs completely and thoroughly come incontact with the main spring becomes 1190 kg. Thus the spring providedwith the round bar steel auxiliary springs is lighter than that providedwith the flat steel auxiliary spring. In practice, because of the factthat such a flat steel as of 50 x 15.6 is unavailable, but a flat steelof 50 x 8 may be used, 8 being the maximum thickness, and requires alamination of several sheets, the spring becomes still heavier.

In FIGS. 5 through 8; another embodiment of this invention isillustrated where an auxiliary spring comprises two round ba-r steelsprings, each having lateral vertical flat sides. While the main spring21 comprises a number of leaf springs 21b quite similarly to thepreceding example, the flat-sided round bar steel springs 43 of theauxiliary spring differs somewhat from the preceding example. Thefiat-sided round bar steel springs 43 vertically have less curvaturethan the curvature of the leaf springs 21b of the main spring 21. Bothends of the fiat-sided round bar steel spring 43 are taperedhorizontally at the lower side 25 whereby the auxiliary spring is mademore easily deflectable when it becomes into contact with the lower-mostleaf spring 27 of the main spring 21. The two flat-sided round bar steelsprings 43 are arranged longitudinally side by side with a spacebetween. The center of the auxiliary spring is provided with a holdingpiece 47 which is welded to the flat-sided round bar steel springs 43. Acenter bolt 49 is provided extending through the leaves 21b of the mainspring 21 and the holding piece 47 with a nut 29b thereon so as tosecure the fiat-sided round bar steel spring 43 in contact with thecentral bottom surface of the lowermost leaf spring 27. Clips 53 areprovided at the inner ends of the tapered parts 25 of the auxiliarysprings 43, respectively. The clip 53 is a top-opened rectangular memberadapted to surround the main spring 21. An upstanding stud 51 is fixedto the clip 53 at the center thereof. The top of the stud 51 is extendedlaterally as an integral spacer 55. The lateral ends of the spacer 55are welded to the auxiliary springs 43, respectively. The tops of theclip 53 are extended upwards above the main spring 21 where the top endsare connected with each other by means of a pin 59. By virtue of this,the two flat-sided round bar steel springs 43 are spaced properly witheach other. It is to be noted that there is a clearance between the clip53 and the main spring 21.

This embodiment also will now be compared with the prior art. If aspring constant required for the auxiliary spring is 2 kn and the suflixfor the fiat steel is f and for this embodiment is s,

in case of flat steel as (l) and (6), and

kn=3E x 2I /L in case of this embodiment. From (6) and (10) l =2l Hence[MR/12:2 x b t /12 Hence The weights will now be compared with eachother by comparing volumes:

The volume of the flat steel,

V =t b L and the volume of the flat sided round bar steel,

V =2b t L Hence V /V .,=t b /2b t (12) From (11) and (12) V /V z2b t /(tx2b t )=b /t (13) Now the minimum value for the breadth b of the Hatsteel is 45 mm. and the minimum value for the thickness t of the same is16 mm. Therefore, the Equation 13 is calculated as whereby it is seenthat the flat-sided round bar steel spring is far lighter than the flatsteel spring, the flat side of the former being arranged vertically.Practically speaking, the desired rigidity is satisfied only bylaminating a number of leaves. In view of this, the flat-sided round barsteel is still more advantageous. Furthermore, since b t, in case of thefiat-sided round bar steel, l b t 12 so that it is readily possible toobtain a leaf having a high rigidity.

It is most rational and effective for lightening a spring that thestress of the auxiliary spring be utilized to the same extent with thestress of the main spring in a progressive spring, so that the flatsteel leaves are, however, used even if the flat side of the flat-sidedround bar steel spring is arranged vertically and made to have a highrigidity. By virtue of such an arrangement it is possible to obtain aprogressive leaf spring which satisfies a desired load characteristic.

In FIG. 10, some load characteristics are plotted in which the curveKrepresents a usual main spring which is not accompanied by an auxiliaryspring. A truck provided with such a spring does not have comfortableriding qualities when unloaded. The curve M represents an im provedusual progressive spring which does not bear the maximum load in view ofstress. In this case, a rubber spring is also provided for a larger loadthan a point In in that curve. If the rubber spring is not provided, thecurve M extends towards the curve L. The curve P represents thisembodiment which is similar to but better than the curve M.

The weights of these springs are compared with each other as folows:

In case of the usual spring represented by the curve K,

zxbxn 8x70'x9 W kg 32.49 kg.

In case of a usual spring provided with a rubber helper represented bythe curve M,

7 x 7 O X 4 t X b x n 6 x x 2 +rubber helper.

W kg 27.95 kg.+rubber helper. In case of this embodiment represented bythe curve P,

7 x 70 x 5 txbxn 45x8x2 W kg 25.48 kg.

The above indicates that the weight of this embodiment represented bythe curve P in FIG. 10 is 78.5 percent of the weight of the usual springrepresent by the curve K and 91 percent of that of the springrepresented by the curve M which additionally requires a rubber helper.The cost of this embodiment therefore is inexpensive by virtue of theconsiderable lightening.

While particular embodiments of this invention have been illustrated anddescribed, modifications thereof will readily occur to those skilled inthe art. It should be understood therefore that the invention is notlimited to the particular arrangements disclosed but that the appendedclaims are intended to cover all modifications which do not depart fromthe true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A spring device comprising a main spring member having a plurality oflaminated spring leaves with an initial upward curvature between theirends,

an auxiliary spring member having a lesser initial curvature between itsends than said spring leaves and being connected at its center to thecenter of said main spring member and in contact with the central bottomsurface of the lowermost leaf of said spring leaves at the center,

7 said auxiliary spring member comprising a plurality of parallelhorizontally spaced bar steel springs extending longitudinally withrespect to lowermost leaf, said bar steel springs at a plurality oflocations including contiguous to their ends having members forretaining said bar steel springs in spaced relation and fromdisplacement.

2. A spring device as defined in claim 1 in which said bar steel springshave horizontally tapered ends beyond said last members.

3. A spring device as defined in claim 1 in which said bar steel springsare round bars.

4. A spring device as defined in claim 2 in which said bar steel springsare round bars having longitudinal vertical flat sides.

References Cited by the Examiner UNITED STATES PATENTS 1,549,455 8/1925Cox 267--47 1,603,564 10/1926 Vesely 26745 2,861,798 11/1958 Lenet etal. 26745 3,053,527 9/1962 Hallam 267-47 ARTHUR L. LA POINT, PrimaryExaminer.

R. M. WOHLFARTH, Assistant Examiner.

1. A SPRING DEVICE COMPRISING A MAIN SPRING MEMBER HAVING A PLURALITY OFLAMINATED SPRING LEAVES WITH AN INITIAL UPWARD CURVATURE BETWEEN THEIRENDS, AN AUXILIARY SPRING MEMBER HAVING A LESSER INITIAL CURVATUREBETWEEN ITS ENDS THAN SAID SPRING LEAVES AND BEING CONNECTED AT ITSCENTER TO THE CENTER OF SAID MAIN SPRING MEMBER AND IN CONTACT WITH THECENTRAL BOTTOM SURFACE OF THE LOWERMOST LEAF OF SAID SPRING LEAVES ATTHE CENTER, SAID AUXILIARY SPRING MEMBER COMPRISING A PLURALITY OFPARALLEL HORIZONTALLY SPACED BAR STEEL SPRINGS EXTENDING LONGITUDINALLYWITH RESPECT TO LOWERMOST LEAF, SAID BAR STEEL SPRINGS AT A PLURALITY OFLOCATIONS INCLUDING CONTIGUOUS TO THEIR ENDS HAVING MEMBERS FORRETAINING SAID BAR STEEL SPRINGS IN SPACED RELATION AND FROMDISPLACEMENT.